1. Field of the Invention
This invention relates generally to biocompatible materials, such as polymers or metals, and more particularly, to biocompatible materials having blood interface surfaces that are capable of biocatalytic or biomimetic generation of nitric oxide in situ when contacted with endogenous nitrite, nitrate, or nitrosothiols in blood.
2. Description of the Related Art
Although medical devices such as extracorporeal circuits and hemodialysis tubes are widely used in clinical settings, the polymers typically used to fabricate such devices (PVC, polyurethane, silicone rubber, etc.) are still subject to platelet aggregation and adhesion onto the surface of these materials. Thus, patients are often given anti-clotting agents (i.e., heparin) in order to reduce thrombosis on the surface of these devices. Similarly, implanted devices made of stainless steel or other alloys, or even carbon, can cause thrombus formation when in direct contact with blood. There is, therefore, a need for materials that more closely simulate the antithrombogenic properties of the endothelial cells that line blood vessels in order to obviate the need to administer anticoagulants.
Nitric oxide (NO) is an important intracellular and intercellular messenger molecule that plays an important physiological role in anti-platelet aggregation and anti-platelet activation, vascular relaxation, neurotransmission, and immune response. It has been proposed that synthetic materials that release low levels of NO would, therefore, more closely simulate the natural activity of endothelial cells, and therefore, would have improved biocompatibility.
Several classes of NO-releasing materials are currently under investigation worldwide. These include NO donors (i.e., diazeniumdiolates, nitrosothiols) that may be relatively complicated to synthesize and may, in some instances, require stringent storage conditions. Thus, there is a need for improved materials that are easier to fabricate and store.
Currently, NO generation is determined by water uptake (such as in the case of diazeniumdiolates) or the intensity of light (as with iron nitrosyls). However, blood already contains a host of species that are derived from, or are physiologically-generated in vivo that can be reduced to NO. These species include nitrites, nitrates, and a host of nitrosothiols (e.g., nitrosoglutathione, nitroso albumin, etc.). This raises the possibility of recycling these species back to nitric oxide. There is, therefore, a need for materials that can reduce these species to nitric oxide locally at the substrate/blood interface.
It is an object of this invention to provide improved materials for biomedical applications that are capable of releasing NO from blood-contacting surfaces materials, so as to prevent platelet activation and adhesion onto these surfaces, thereby lowering thrombus formation and other complications associated with interactions between blood and foreign materials.
It is a further object of this invention to provide improved materials for biomedical applications that are relatively inexpensive to manufacture and that have improved biocompatibility.
It is still a further object of this invention to provide materials for biomedical applications that are capable of releasing NO from blood-contacting surfaces materials in response to nitrites, nitrates, and nitrosothiols in the blood.